This invention relates to a projection apparatus of rear-projection type (such as a rear projector) having an optical engine that projects an image from a rear side of a transmission-type screen. In particular, this invention relates to a projection apparatus having an adjusting mechanism for adjusting an angle at which the image is projected.
In a projection apparatus generally known as a rear projector, a transmission-type screen is provided on a front surface of a housing, and an optical engine that projects an image from a rear side of the transmission-type screen is placed in the housing. An angle at which the optical engine projects the image is adjusted so that the image is projected in an appropriate direction.
In the manufacturing process of the rear projector, there may be individual differences in the shape of the housing and dimension errors, assembling errors and deformation of respective components mounted in the housing. For these reasons, the contour of the displayed image may be varied, and the angle at which the image is projected on the transmission-type screen may be varied. As a result, the position of the projected image may deviate from the ideal position, or the image may be deformed. Further, in the general manufacturing process of the conventional rear projector, the optical engine that forms the image is directly mounted in the housing. Therefore, in order to correct the displacement or deformation of the image projected on the transmission-type screen (due to the variation of the projection angle) after the optical engine is mounted in the housing, it is necessary to adjust the position of an image display device such as liquid crystal display or digital mirror device (DMD) provided in the optical engine, or to adjust the angle of a projection optical system such as a projection lens, a reflection mirror or the like. In this case, the position or angle of the relatively small components must be adjusted, and therefore the adjustment is difficult to operate.
In order to facilitate the adjustment of the projection angle, there is proposed a rear projector in which an engine supporting plate for placing the optical engine and a supporting table with an inclination position adjusting mechanism capable of adjusting the inclination angle of a supporting surface of the supporting plate are provided in the housing. After the optical engine is placed on the engine supporting plate, the inclination angle of the engine supporting plate is adjusted by means of the inclination position adjusting mechanism of the supporting table to adjust the orientation of the optical engine. With this, the projection angle is adjusted and the deformation of the image displayed on the transmission-type screen is corrected, so that the entire image displayed on the transmission-type screen is optimized. Such a rear projector is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2003-337379 (see, paragraph 0008 and FIG. 13).
For example, with the inclination position adjusting mechanism disclosed in the above described publication, the lengths of screws of two predetermined rods selected among four rods (i.e., adjusting mechanism) disposed on four corners of the engine supporting plate are adjusted in synchronization with each other, so as to adjust the angle of the engine supporting plate in the vertical direction about a predetermined horizontal axis. Further, in order to enable the adjustment of the inclination of the optical engine in the horizontal direction (left-to-right direction), the engine supporting plate has two-layer structure and the upper plate is slidable. The inclination of the optical engine in the horizontal direction can be adjusted by slidably adjusting the upper plate with respect to the lower plate, and by fixing the upper plate to the lower plate using screws.
However, with the above described inclination position adjusting mechanism, it is necessary to adjust the lengths of the screws of two rods (among four rods) in synchronization with each other for adjusting the angle about the predetermined horizontal axis in the manufacturing process, and therefore the adjusting operation takes a long time. Moreover, in order to horizontally rotate (adjust) the engine supporting plate about the axis perpendicular to the surface of the engine supporting plate, the engine supporting plate need to have two layer structure and the upper plate need to be slidable. Therefore, the rear projector has a complicated structure and includes a large number of components, with the result that the rear projector becomes heavier and more expensive.